Will natural resources comprise an important constraint on economic development in the 21st century? We use a macroeconomic model (MAVA) to demonstrate the precise nature of this problem. First, we employ the model to demonstrate that resource constraints do not substantially limit future economic growth under parametric conditions prevailing in the period 1960–2010. Second, we examine the sorts of changed conditions that are unavoidable in the coming century and demonstrate that declining population growth (and the increased dependency rates this implies) is likely to result in increasingly important resource constraints. Ironically, it is the decline in population growth rates-and not the opposite-that may occasion the return of Malthusian constraints.